Lubricant composition

ABSTRACT

A lubricant composition including (a) a first low viscosity polyalkylene oxide based fluid such as a combination of propylene oxide (PO) and butylene oxide (BO) based fluid with a first alcohol as an initiator; wherein the first low viscosity PO/BO based fluid has a number average molecular weight of less than about 5 600 Da; and (b) a second high viscosity polyalkylene oxide based fluid such as a combination of ethylene oxide (EO) and propylene oxide (PO) based fluid with a second alcohol as an initiator; wherein the second high viscosity EO/PO based fluid has a number average molecular weight greater than about 600 Da; a process for manufacturing the above lubricant; and a driveline fluid made from the above lubricant composition.

FIELD

The present invention is related to a lubricant composition; and more specifically, to a polyalkylene oxide-based lubricant composition that exhibits improved properties when used in applications such as for gear lubricants.

BACKGROUND

Heretofore, mineral oil-based lubricants (Groups I, II and III base oils) and polyalphaolefin (PAO)-based lubricants (Group IV base oils) have been used as driveline fluids for applications such as engine oil, axle oils, and transmission fluids for decades. For some of the applications, the known fluids are characterized as “fill for life” meaning that once the lubricant has been incorporated into a vehicle no oil change is required over the useful life of the vehicle. The 2025 CAFE (Corporate Average Fuel Economy) regulations related to the requirement that automobiles perform at 54.5 miles per gallon (mpg) are prompting original manufacturers (OEMs) to look at different compositions of lubricants as a possible option that can further enhance fuel economy without compromising durability.

One approach to improve the fuel economy of an automobile is to improve the lubricant fluid used as gear lubricants for axles, transfer cases and the like of an automobile. For example, reducing the kinematic viscosity of the lubricant from about 11-12 centistokes (cSt) to about 5-6 cSt will, in turn, reduce spinning losses by about 50 percent (%) to about 60%; and will reduce power losses by about 30% to about 40%, thereby achieving an improvement in fuel economy of from about 1% to about 2%. The challenge with the above approach is that reducing the viscosity of a lubricant can result in thin films which will cause metal to metal contact which will ultimately cause higher friction and wear that can result in premature failures, for example, of a gear system.

In an attempt to solve the above problems, conventional compounds known as “viscosity modifiers” have been added to conventional mineral oil-based oils (Groups I, II and III base oils) to try to impart to the oils a high viscosity index (V.I.) (e.g., a V.I. of from about 170 to about 190) which, in turn, would provide oils with a low dynamic viscosity at a low temperature that would help to reduce spinning losses. However, there is a limit to the use of V.I. improvers (viscosity modifiers) because such V.I. improvers have a tendency to shear degrade over a period of time that causes permanent viscosity loss of lubricants. Fluids (lubricants) with a V.I. of up to 180 have been used in the industry with the help of viscosity modifiers to achieve a low viscosity (e.g., <70,000 centipoise (cP) at −40 degrees Centigrade (° C.) for an 11-12 cSt fluid at 100° C.) at low temperatures. The above known lubricants can also use compounds known as “friction modifiers” such as glycerol oleates for friction reduction of the lubricant to achieve energy efficiency.

Another challenge with the use of Groups I to III base oils is that such oils have a high pour point; and hence, an additive known as a “pour point depressant” is required to be added to the oils to achieve the desired viscosities at −40° C. of such oils such that pumping losses of the oils at a low temperature are minimized. Pumping losses are the energy losses due to moving a liquid through a device. Higher viscosity liquids require more energy to move (pump) than lower viscosity liquids. At start-up conditions a higher viscosity liquid will take more energy to move, resulting in higher fuel consumption.

Heretofore, in an attempt to solve the above problem of pumping losses and to maximize the decrease of pumping losses, Group IV base oils such as polyalphaolefin base fluids have been used in place of Groups I to III base oils because Group IV base oils inherently have, for example: (1) a good low temperature property, (2) a better V.I. compared to Group III base oils, and (3) a lower traction coefficient compared to Group III oils. In addition, Group IV base oils in combination with V.I. improvers and friction modifiers provide a better alternative compared to Group III base oils in achieving fuel economy. Fluids (lubricants) with a V.I. of up to 190 have been used in the industry with the help of V.I. improvers and friction modifiers to achieve energy efficiency.

Group V base oils, such as polyalkylene oxide based oils made from 50/50 ethylene oxide (EO)/propylene oxide (PO) with butanol as the initiator, have inherently a higher V.I. compared to Group III and Group IV base oils (e.g., from about 30% to about 40% higher); and the Group V base oils also have a significantly lower (e.g., from about 30% to about 50% lower) traction coefficients and hence are ideally suited for applications where energy efficiency is required. One of the challenges with the Group V base oils is that these fluids have a 15-20% higher density compared to Group III base oils and Group IV base oils. And, the higher density of the Group V base oils increases the dynamic viscosity at low temperatures (e.g., from about 20° C. to about 60° C.). The churning losses are directly proportional to the dynamic viscosity; and hence, when the performance of formulated alcohol initiated 50/50 EO/PO fluids without the use of V.I. improvers is compared with formulated Group III and Group IV base oil with V.I. improvers, the churning losses at low temperatures (e.g., from about 20° C. to about 60° C.) are similar. Therefore, the only benefit obtainable with the use of a formulated alcohol initiated 50/50 EO/PO fluid (e.g., UCON™ 50-HB fluid; a trademark of The Dow Chemical Company) is from about a 30% to about 50% lower traction coefficient which can help in achieving energy efficiency to only a limited extent.

“Churning” or “spin” losses are energy losses due to a mechanical element (gear) spinning in a liquid (oil). The drag forces are calculated using the following equation:

Force=C _(d) *v ² *ρ*A.

In above equation, C_(d) is the drag coefficient and is a function of the Reynolds number, V is velocity of the spinning element, p is the density of the liquid, and A is a characteristic wetted cross sectional area.

Mixtures of polyalkylene oxides are known in general. However, a specific mixture of butanol initiated EO/PO copolymers and dodecanol initiated PO/butylene oxide (BO) copolymers has heretofore not been disclosed. Some lubricant formulations are known as “oils of lubricating viscosity” and such “oils of lubricating viscosity” are frequently defined as “Groups I, II, III, IV and V base oils”. Of the Group V base oils, polyalkylene oxides and esters are generally specified as Group V base oils. And, the known polyalkylene oxides are further defined generally as including diether, monol, diol, C1-C20 alcohol initiated, any and all combination of EO/PO/BO and higher oxides in any ratio, and polymer blends thereof. However, the prior art does not disclose specific blends of butanol initiated EO/PO copolymers and dodecanol initiated PO/BO copolymers at ratios required to maintain the miscibility of such copolymer components. Not all blends of polyalkylene glycols are miscible, such immiscible blends are impractical for use as a lubricant base stock. Typically, a required additive or combination of additives is added to the lubricant formulation to make the formulation useful.

SUMMARY

The present invention, in one embodiment, is directed to a lubricant composition including: (a) a first low viscosity polyalkylene oxide based fluid with a first alcohol as an initiator; wherein the first low viscosity polyalkylene oxide based fluid has a number average molecular weight of less than about 600 Da; and (b) a second high viscosity polyalkylene oxide based fluid with a second alcohol as an initiator; wherein the second high viscosity polyalkylene oxide based fluid has a number average molecular weight greater than about 600 Da; and wherein the first low viscosity polyalkylene oxide based fluid is different from the second high viscosity polyalkylene oxide based fluid.

The problems of known lubricant compositions of the prior art are addressed by the present invention lubricant composition. The present invention lubricant composition provides important and beneficial properties including for example: (i) a low temperature viscosity (e.g., −40° C. dynamic viscosity of less than 40,000 cP for an 11-12 cSt fluid at 100° C.), (ii) a high viscosity index (e.g., a viscosity index of greater than (>215), and (iii) a low traction coefficient inter alia.

In another embodiment, the process of manufacturing the above lubricant composition is provided herein.

In still another embodiment, the present invention is directed to the use of the above lubricant composition in a driveline fluid.

DETAILED DESCRIPTION

As described in ASTM D2270, viscosity index, abbreviated V.I. and used with reference to a lubricant composition in this disclosure, is an arbitrary number used to characterize the variation of the kinematic viscosity of a petroleum product with temperature. For oils of similar kinematic viscosity, the higher the V.I. the smaller the effect of temperature on its kinematic viscosity. The V.I. number is a widely used and accepted measure of the variation in kinematic viscosity due to changes in the temperature of a petroleum product between 40° C. and 100° C. A higher V.I. indicates a smaller decrease in kinematic viscosity with increasing temperature of the lubricant. The V.I. is used in practice as a single number indicating temperature dependence of kinematic viscosity. V.I. is sometimes used to characterize base oils for purposes of establishing engine testing requirements for engine oil performance categories.

Dynamic viscosity, with reference to a lubricant composition, herein means a viscosity as measured by a Stabinger viscometer in units of mPa s. See ASTM D 7042, “Standard Test Method for Dynamic Viscosity and Density of Liquids by Stabinger Viscometer (and the Calculation of Kinematic Viscosity)”.

“Pour point” herein, with reference to a lubricant composition and petroleum products, means the lowest temperature at which movement of the test specimen is observed under prescribed conditions of test. The units of this measurement are in ° C. Pour point can be measures using the procedure described in ASTM D 6892, “Standard Test Method for Pour Point of Petroleum Products (Robotic Tilt Method)”.

“Traction” is a force transmitted through a lubricant film between to surfaces in relative motion. A “traction coefficient” is the measured traction force/normal applied force.

As used herein, Group I, II, III, IV and/or V base oils are those as defined by the American Petroleum Institute (Annex E-API Base Oil Interchangeability Guidelines for Passenger Car Motor Oils and Diesel Engine Oils, March 2015 Version).

In its broadest scope, the present invention includes a lubricant composition including: (a) a first low viscosity polyalkylene oxide based fluid with a first alcohol as an initiator; wherein the first low viscosity polyalkylene oxide based fluid has a number average molecular weight of less than about 600 Da; and (b) a second high viscosity polyalkylene oxide based fluid with a second alcohol as an initiator; wherein the second high viscosity polyalkylene oxide based fluid has an average molecular weight greater than about 600 Da; and wherein the first low viscosity polyalkylene oxide based fluid is different from the second high viscosity polyalkylene oxide based fluid. The number average molecular weights provided herein are as reported by manufacturer.

The viscosity of the first low viscosity polyalkylene oxide based fluid, in general, can be from about 2 cSt to about 8 cSt in one embodiment, from about 2 cSt to about 6 cSt in another embodiment, and from about 2 cSt to about 4 cSt in still another embodiment. The kinematic viscosity is calculated according to ASTM D 7042.

The first low viscosity polyalkylene oxide based fluid with a first alcohol as an initiator, in general, has a number average molecular weight of less than about 600 Da in one embodiment, less than about 550 Da in another embodiment, and less than about 400 Da in still another embodiment.

The polyalkylene oxide of the first low viscosity polyalkylene oxide based fluid can include for example, a polyethylene oxide, a polypropylene oxide, a polybutylene oxide, polyalkylene oxide copolymers derived from EO/PO/BO and polymer mixtures thereof. For example, in one embodiment the first low viscosity polyalkylene oxide based fluid is a combination of a propylene oxide and a butylene oxide. In another embodiment, for example, the combination of a propylene oxide and a butylene oxide to arrive at a first low viscosity polyalkylene oxide based fluid can include a 50/50 propylene oxide/butylene oxide based fluid (wt. % basis).

The first low viscosity polyalkylene oxide based fluid may include a lower molecular weight capped oil soluble polyalkylene oxides (e.g., a capped UCON™ OSP, an oil soluble polyalkylene oxide having less than about 600 Da average molecular weight, where UCON™ is a trademark of The Dow Chemical Company). As used herein, capped indicates that the terminal hydroxyl groups of the polyalkylene oxide(s) are substituted with a hydrocarbyl group of C1 to C12 or a C8 alkyl phenyl group (i.e., a benzyl group). Preferably, capped oil soluble polyalkylene oxides are substituted with a C1 to C4 hydrocarbyl group.

Generally, the first low viscosity polyalkylene oxide based fluid (the “low viscosity fluid”) used as component (a) of the lubricant composition, includes for example UCON™ OSP-12 (a C12 alcohol initiated 50/50 PO/BO UCON™ OSP fluid with 3 cSt viscosity at 100° C., commercially available from The Dow Chemical Company), UCON™ OSP-18 (a C12 alcohol initiated 50/50 PO/BO UCON™ OSP fluid with 4 cSt viscosity at 100° C. and 550 Da), and mixtures thereof. The first low viscosity polyalkylene oxide based fluid may also be formed using a C4-C18 alcohol initiator, where different ratios of PO/BO can be used.

In a preferred embodiment, the low viscosity fluid useful in the lubricant composition of the present invention may include for example, UCON™ OSP-12 (a C12 alcohol initiated 50/50 PO/BO UCON™ OSP fluid with 3 cSt viscosity at 100° C.).

The concentration of the low viscosity fluid used in the lubricant composition of the present invention may range generally from about 30 weight percent (wt %) to about 90 wt % in one embodiment, from about 40 wt % to about 80 wt % in another embodiment, and from about 50 wt % to about 70 wt % in still another embodiment, based on the total weight of the components in the lubricant composition. When the concentration of the low viscosity fluid is greater than 80 wt % concentration, it is difficult to achieve a target viscosity of 11-12 cSt at 100° C.; and even if it were possible to achieve the target viscosity, the V.I. of the resulting fluid is lower.

The first alcohol initiator useful for the first low viscosity polyalkylene oxide based fluid can include for example, an alcohol selected from ethanol, methanol, propanol, butanol, dodecanol, and mixtures thereof.

The viscosity of the second high viscosity polyalkylene oxide based fluid, in general, can be from about 16 cSt at 100° C. to about 250 cSt at 100° C. in one embodiment, from about 25 cSt at 100° C. to about 164 cSt at 100° C. in another embodiment, and from about 25 cSt at 100° C. to about 70 cSt at 100° C. in still another embodiment.

The second high viscosity polyalkylene oxide based fluid with a second alcohol as an initiator, in general, has a number average molecular weight of greater than about 600 in one embodiment, greater than about 2,000 in another embodiment, and greater than about 2,660 in still another embodiment.

Generally, the second high viscosity polyalkylene oxide based fluid (the “high viscosity fluid”) used as component (b) of the lubricant composition includes for example a 50/50 EO/PO copolymer blend having a molecular weight in the range of from about 1,590 Da (e.g., UCON™ 50-HB-660, commercially available from The Dow Chemical Company) to about 3,930 Da (e.g., UCON™ 50-HB-5100, commercially available from The Dow Chemical Company); and mixtures thereof. The second high viscosity polyalkylene oxide based fluid also includes for example a 45/55 EO/PO copolymer blend with molecular weight in the range of from about 1,590 Da to about 3,930 Da.

In a preferred embodiment, the high viscosity fluid useful in the lubricant composition of the present invention may include for example, UCON™ 50-HB-2000 (a 50/50 EO/PO copolymer commercially available from The Dow Chemical Company) with butanol as initiator and molecular weight of 2,660 Da; SYNALOX™ 55-150B (a 45/55 EO/PO copolymer blend, commercially available from The Dow Chemical Company) with butanol as the initiator and molecular weight of 2,200 Da; and mixtures thereof.

The concentration of the high viscosity fluid used in the lubricant composition of the present invention may range generally from about 10 wt % to about 70 wt % in one embodiment, from about 20 wt % to about 60 wt % in another embodiment, and from about 30 wt % to about 50 wt % in still another embodiment, based on the total weight of the components in the lubricant composition. When the concentration of the high viscosity fluid is greater than 50 wt % concentration, the resulting fluid will have a viscosity of greater than about 11-12 cSt target viscosity at 100° C.

The ratio of component (a) such as UCON™ OSP-12, UCON™ OSP-18 to component (b) such as UCON™ 50-HB-2000, UCON™ 50-HB-3520, UCON™ 50-HB-5100 or SYNALOX™ 55-150B, can be generally from about 90 to about 10 in one embodiment; from about 70 to about 30 in another embodiment; and from about 50 to about 50 in still another embodiment.

The second alcohol useful as an initiator for the second high viscosity polyalkylene oxide based fluid can include for example, an alcohol selected from ethanol, methanol, propanol, butanol, dodecanol, alcohols up to a carbon chain length of 18 (C18), and mixtures thereof. The second alcohol can also be alcohols with mixed chain lengths. The second initiator alcohol, when used, is different than the first initiator alcohol.

The lubricant composition of the present invention may also include any number of optional components such as for example one or more of antioxidants; antiwear compounds; extreme pressure, rust and corrosion inhibitors; sulfur scavengers; detergents; dispersants; antifoaming additives; and mixtures thereof.

The concentration of the optional additives for the lubricant composition of the present invention may range generally from 0 wt % to about 20 wt % in one embodiment, from about 0.01 wt % to about 10 wt % in another embodiment, and from about 0.1 wt % to about 5 wt % in still another embodiment, based on the total weight of the components in the lubricant composition.

The process and type of equipment used to prepare the lubricant composition of the present invention includes blending or mixing of the above components in conventional mixing equipment or vessels known in the art. For example, the preparation of the lubricant composition of the present invention is achieved by blending, in known mixing equipment, (a) the low viscosity fluid, and (b) the high viscosity fluid, and (c) optionally any other desirable additive.

All the above compounds of the lubricant composition are typically mixed and dispersed in a vessel at a temperature enabling the preparation of an effective working lubricant fluid. For example, the temperature during the mixing of the above components may be generally from about 25° C. to about 75° C. in one embodiment, and from about 25° C. to about 55° C. in another embodiment. Components (a)-(c) of the present invention are miscible at room temperature (about 25° C.) and at low temperatures. (e.g., down to about −5° C.).

The preparation of the lubricant composition of the present invention, and/or any of the steps thereof, may be a batch or a continuous process. In a preferred embodiment, the mixing process of the components for preparing the lubricant composition; and the mixing equipment used in the process may be any vessel and ancillary equipment well known to those skilled in the art.

In one embodiment, the present invention includes a combination or blend of at least two components including, for example: (a) a first low viscosity (e.g., less than about 4 cSt) polyalkylene oxide based fluid made from a combination of at least two different polyalkylene oxide fluids with a first alcohol such as dodecanol as the initiator and a average molecular weight of less than about 600 Da; and (b) a high viscosity (e.g., greater than about 4 cSt) polyalkylene oxide based fluid made from a combination of at least two different polyalkylene oxide fluids with a second alcohol such as butanol as the initiator and a number average molecular weight of greater than about 600 Da. This unique combination or mixture of two different polyalkylene oxide based fluids of the present invention, one having a low viscosity and the other having a high viscosity, provides several benefits including based fluids having a low density, a high V.I. index, a low traction coefficient, and good low temperature properties. One of the surprising results of the fluid mixture of the present invention is that the low temperature property at −40° C. of the combination of a low and a high viscosity or molecular weight polyalkylene oxide base fluids as previously defined is better than the baseline or control polyalkylene oxide fluid.

In one preferred embodiment, for example, the present invention includes a blend of at least two components including (a) a first low viscosity 50/50 PO/BO based fluid with a first alcohol such as dodecanol as the initiator and the fluid having a number average molecular weight of less than about 580 Da; and (b) a second high viscosity 50/50 EO/PO or 45/55 EO/PO based fluid with a second alcohol such as butanol as the initiator and the fluid having a number average molecular weight greater than about 2,660 Da. For example, SYNALOX™ 55-150B, which can be one embodiment of the second high viscosity 50/50 EO/PO or 45/55 EO/PO based fluid, has a molecular weight of about 2,200 Da.

By using a combination of the above described EO/PO and PO/BO based fluids in a lubricant composition, beneficial properties are imparted to the lubricant composition including for example, the composition has: (1) a higher V.I. for the same 100° C. viscosity base oil compared to a dodecanol initiated 50/50 PO/BO base fluid and butanol initiated 50/50 EO/PO base fluid; (2) a lower traction coefficient compared to dodecanol initiated 50/50 PO/BO base fluid and similar traction coefficients compared to butanol initiated 50/50 EO/PO base fluid; (3) a higher V.I. compared to dodecanol initiated 50/50 PO/BO base fluid and butanol initiated 50/50 PO/BO base fluid; (4) a lower dynamic viscosity at −40° C. and 40° C. compared to butanol initiated 50/50 EO/PO base fluid and dodecanol initiated 50/50 PO/BO base fluid; and (5) a lower density compared to the 50/50 EO/PO base fluids.

One of the surprising results of the lubricant composition of the present invention is that the properties of the composition at sub-zero temperature, e.g., at a temperature of about −40° C., are better (e.g., less than about 40,000 cP at −40° C. for a 11-12 cSt fluid at 100° C.) than the baseline 50/50 EO/PO based fluid. For example, using the unique combination of the above described two fluids in a lubricant composition, provides the composition with a higher V.I. (e.g., up to about 229 V.I.), a lower dynamic viscosity (e.g., from about 10% to about 20% lower dynamic viscosity) over the operating temperature range of from about 20° C. to about 100° C., a lower traction coefficient for base fluids, and extremely good low temperature properties, without the need to use pour point depressants or V.I. improvers.

In one embodiment, the present invention is directed to a lubricant composition with a target 11-12 cSt viscosity at 100° C. including: (a) a low viscosity (e.g., a viscosity of from about 2 cSt to about 4 cSt at 100° C.) 50/50 PO/BO based fluid with dodecanol as the initiator and molecular weight of less than about 580 Da; and (b) a high viscosity (e.g., a viscosity of greater than about 25 cSt at 100° C.) 50/50 EO/PO based fluid with butanol as the initiator and a molecular weight greater than about 1,500 Da; wherein the lubricant composition has a viscosity index of greater than about 215; a dynamic viscosity of lower than about 40,000 cP at a temperature of −40° C.; and a lower traction coefficient for the base fluid in the absence of a pour point depressant or a V.I. improver. Examples of the low viscosity 50/50 PO/BO based fluid include the UCON™ OSPs and their capped analogs, as both discussed herein, and examples of the high viscosity 50/50 EO/PO based fluids include UCON™ 50-HB fluids and their capped analogs, also as both discussed herein.

In one preferred embodiment, the lubricant composition of the present invention relates to compositions of a polyalkylene oxides based base oil wherein a PO/BO co-polymer with a dodecanol initiator and with a molecular weight of less than or equal to about 550 Da is mixed with a EO/PO co-polymer with a butanol initiator and with a molecular weight of greater than about 2,000. The mixing ratios can vary, for example, a 67/33 (UCON™ OSP-18/UCON™ 50-HB-2000) ratio can be used to achieve a lubricant composition's target viscosity of about 11-12 cSt at 100° C. for applications such as gear oils. In another example, an 87/13 (UCON™ OSP-128/UCON™ 50-HB-2000) ratio can be used to achieve a lubricant composition's target viscosity of about 6 cSt at 100° C. to target applications such as gear oils, ATF oils, or engine oils in transportation applications.

The lubricant composition prepared by the above process of the present invention exhibits several unexpected and unique properties. For example, the dynamic viscosity of the lubricant composition of the present invention is such that the composition can be easily handled and processed. The lubricant composition with a 11-12 cSt kinematic viscosity at 100° C. may have a dynamic viscosity in the range of from about 45 millipascals second (mPa-s) to about 60 mPa-s at 40° C. in one embodiment, from about 47 mPa-s to about 55 mPa-s at 40° C. in another embodiment, and from about 47 mPa-s to about 52 mPa-s at 40° C. in still another embodiment. Greater than 60 mPa-s at 40° C. does not provide any improvement in fuel economy.

Another property that the lubricant composition exhibits is a high V.I. value. Generally, the V.I. property can be between 209 and 229 in one embodiment, between about 215 and 229 in another embodiment, and between about 220 and 229 in still another embodiment. Below a V.I. of 209 for the combination mixture, the 40° C. dynamic viscosities are similar to compounds similar to the UCON™ 50-HB series of copolymers and lower spinning losses cannot be achieved.

In another embodiment, the V.I. of the composition may be further increased by using a low viscosity base oil as defined above which is a C12 alcohol initiated PO/BO polyalkylene oxide diether or capped base oil. It is known that the use of capped base oils as the lower molecular weight component can impact the solubility of the overall composition. Since homogenous mixtures are desirable, the solubility of the C12 alcohol initiated PO/BO polyalkylene oxide diether component can be further improved in the higher molecular weight base oil, if necessary. Examples of modification of the higher molecular base oil include, but are not limited to, using a longer initiator such as a C12 alcohol initiator or by using a combination of longer initiator and capping the EO/PO polymer. The capped 50/50 EO/PO polymer may further enhance the V.I. Another way of improving the solubility of C12 alcohol initiated PO/BO diether is by changing the EO/PO ratio in the higher molecular weight base oil, for example, from 50/50 to 40/60 or 30/70. There may be a limitation on how much the ratio can be altered as adding more PO will increase the traction coefficients and will also adversely affect the −40° C. viscosity.

The lubricant composition can also exhibit a low traction coefficient. Generally, the traction coefficient (e.g., at 80° C. and 500 millimeters per second (mm/s) speed with 150% slide to roll ratio) can be between about 0.025 and about 0.04 in one embodiment, between about 0.025 and about 0.035 in another embodiment, and between about 0.025 and about 0.03 in still another embodiment. The traction coefficients under the same conditions may be between about 0.045 and about 0.05 for a Group III base oil; and between about 0.035 and about 0.04 for a Group IV base oil. The fluids of the present invention have a traction coefficient which is from about 25% to about 30% lower than a Group IV base oil (polyalpha olefin or PAO). Fluids having lower traction coefficients are desired as these fluids may provide benefit in terms of fuel economy. A fluid having a traction coefficient close to 0.035 under these conditions may not provide a fuel economy benefit over a Group IV base oil.

Yet another property that the lubricant composition of the present invention exhibits is an excellent viscosity at a lower temperature, such as −40° C. Generally, the −40° C. dynamic viscosity property can be between about 20,000 cP and about 50,000 cP in one embodiment, between about 20,000 cP and about 40,000 cP in another embodiment, and between about 20,000 cP and about 30,000 cP in still another embodiment without the use of pour point depressants.

After the lubricant composition is prepared as described above, the lubricant composition can be used in various driveline fluids. For example, the lubricant composition can be used for driveline fluids for applications such as engine oil, axle oils, transmissions fluids, worm gear oils, industrial gear oils, and the like.

For applications such as automatic and manual transmission fluids, axle oils and industrial gear oils, the gears are submerged in the lubricant to a certain depth (e.g., a depth of from about 25% to about 50%) for lubrication. For such applications, churning or spinning losses can be significant especially at low temperatures and during start up and such losses can have a negative impact on fuel economy and energy efficiency of an automobile. These churning losses are directly dependent on the dynamic viscosity of the fluid at that temperature and hence reducing the dynamic viscosity can reduce the churning losses. OEM's are contemplating lowering viscosity grade oils for these types of applications to minimize these spinning losses and improve fuel economy. The challenge with going to lower viscosity grades is thinner films and faster transition to boundary and mixed lubrication regime which can cause higher wear and affect the durability and life of the gears. One way to achieve lower viscosity at lower temperatures is by using V.I. improvers but there are limitations when using V.I. improvers due to the shear stability requirement.

To address this problem similar viscosity grades of fluids are targeted; and by taking the advantage of lower density and higher V.I. of UCON™ OSPs (e.g., UCON™ OSP-12 and/or UCON™ OSP-18) and the better traction coefficient of UCON™ 50-HB fluids, unique combinations of fluids can be developed that provide lower dynamic viscosity at low temperatures, significantly improved cold temperature viscosity, and traction coefficients similar to the UCON™ 50-HB fluids. UCON™ OSPs have a 7-8% lower density compared to the UCON™ 50-HB fluids whereas for the same viscosity grades, UCON™ 50-HB fluids have 30% higher VI compared to UCON™ OSP's.

EXAMPLES

The following Examples and Comparative Examples further illustrate the present invention in more detail but are not to be construed to limit the scope thereof.

In the following Examples and Comparative Examples, various terms and designations were used and are explained as follows:

“EO” stands for ethylene oxide.

“PO” stands for propylene oxide.

“BO” stands for butylene oxide.

“UCON™ OSP” stands for oil soluble polyalkylene glycols.

Traction coefficients as reported herein are derived from Stribeck curves formed from data measured on a PCS Mini-Traction Machine using ¾ inch ball on a disc both made of AISI 52100 steel. Both ball and disc had surface finishes of Ra (arithmetical mean deviation) better than 0.01 micron. The measurements were done at 80° C. and 120° C., a load of 50 Newton, a slide to roll ratio (SRR) of 150% and from speeds of 2000 mm/s to 100 mm/s. The test measurements were conducted 12 times in succession at each temperature. The traction coefficient at 500 mm/s+/−2 mms of the 12^(th) repeat was reported.

In the following Examples, the following base oils described in Table I were used for preparing lubricant compositions and for evaluating the performance of such compositions.

TABLE I List of Base Oils BASE OIL CHEMISTRY OF BASE OIL SUPPLIER UCON ™ 50- Butanol initiated 50/50 weight per weight The Dow HB-260 (w/w) EO/PO random co-polymer typical Chemical kinematic viscosity of 11.1 cSt at 100° C. Company UCON ™ 50- Butanol initiated 50/50 w/w EO/PO The Dow HB-400 random co-polymer typical kinematic Chemical viscosity of 16.3 cSt at 100° C. Company UCON ™ 50- Butanol initiated 50/50 w/w EO/PO The Dow HB-2000 random co-polymer typical kinematic Chemical viscosity of 70.2 cSt at 100° C. Company UCON ™ 50- Butanol initiated 50/50 w/w EO/PO The Dow HB-5100 random co-polymer typical kinematic Chemical viscosity of 164 cSt at 100° C. Company UCON ™ Dodecanol initiated 50/50 w/w PO/BO The Dow OSP-12 random co-polymer typical kinematic Chemical viscosity of 3 cSt at 100° C. Company UCON ™ Dodecanol initiated 50/50 w/w PO/BO The Dow OSP-18 random co-polymer typical kinematic Chemical viscosity of 3.9 cSt at 100° C. Company UCON ™ Dodecanol initiated 50/50 w/w PO/BO The Dow OSP-32 random co-polymer typical kinematic Chemical viscosity of 6.5 cSt at 100° C. Company UCON ™ Dodecanol initiated 50/50 w/w PO/BO The Dow OSP-68 random co-polymer typical kinematic Chemical viscosity of 12 cSt at 100° C. Company SYNALOX ™ Butanol initiated BO homo polymer with The Dow OA-25 typical kinematic viscosity of 4.9 cSt at Chemical 100° C. Company SYNALOX ™ Butanol initiated BO homo polymer with The Dow OA-60 typical kinematic viscosity of 9 cSt at Chemical 100° C. Company SYNALOX ™ Butanol initiated 45/55 w/w EO/PO The Dow 55-150B random co-polymer typical kinematic Chemical viscosity of 40-45 cSt at 100° C. Company SYNALOX ™ Diol initiated 60/40 w/w EO/PO random The Dow 40-D300 co-polymer typical kinematic viscosity Chemical of 78 cSt at 100° C. Company

In the following Examples and Comparative Examples, standard measurements, analytical equipment and methods were used to measure the properties of the lubricants as follows:

Dynamic Viscosity, Kinematic Viscosity, and Viscosity Index

A viscometer, Stabinger Viscometer™ SVM 3000, measures the dynamic viscosity and density of oils and fuels according to ASTM D7042. From the above measurements, the viscometer automatically calculates the kinematic viscosity and delivers measurement results which are equivalent to ASTM D445. The Stabinger Viscometer™ SVM 3000 is a rotational viscometer with a cylinder geometry which works according to the modified Couette principle with a rapidly rotating outer tube and an inner measuring bob which rotates more slowly. A 2.5 milliliter (mL) sample is placed in the viscometer and the dynamic viscosity and density are measured as a function of temperature of from about 20° C. to about 100° C.

Cold Temperature Viscosity Measurement

Cold temperature viscosity measurements are obtained using a Brookfield viscometer. The principle of operation of the viscometer is to rotate a spindle (which is immersed in a test sample fluid) through a calibrated spring. The viscous drag of the fluid against the spindle is measured by spring deflection. Spring deflection is measured with a rotary transducer which provides a torque signal. Approximately 7 mL of sample are placed in a cup, containing a number 31 spindle, and placed in a small sample adapter that connects to a Brookfield programmable rheometer. (The software accounts for the specific geometry of this setup). The temperature of the sample is controlled by an external bath that cools the sample to the desired temperature.

Viscosity measurements are made starting at 0° C. and continuing down to −30° C. At each temperature, 3 rotational speeds are selected (based on previous data) to measure the viscosity (each rotational speed is applied for 5 minutes in order to reach steady-state). The measurement that has a torque reading closest to 50% (must be +/−2% for −30° C.) is recorded. A single sample is used to record all desired temperatures (usually 0° C., −10° C., −20° C., −30° C., and −40° C.).

Examples 1-2 and Comparative Examples A-I

Table II describes the composition or formulation of various base fluids. Table III describes the results of evaluating the various formulations with the components listed in Table II. Table III highlights the kinematic and dynamic viscosities, viscosity index, low temperature dynamic viscosity, solubility, and traction coefficients of different combinations of base fluids making up the formulations. All of the fluids have a target viscosity of 11.7 cSt at 100° C.

TABLE II Various Base Fluids C. Ex A Ex. 1 Ex. 2 C. Ex. B C. Ex. C C. Ex. D C. Ex. E C. Ex. F C. Ex. G C. Ex. H C. Ex. I Components Wt % Wt % Wt % Wt % Wt % Wt % Wt % Wt % Wt % Wt % Wt % UCON ™ 50- 80.5000 HB-260 UCON ™ 50- 19.5000 26.9000 HB-400 UCON ™ 50- 33.1000 23.3000 10.0000 31.7000 22.4000 14.4000 29.5000 HB-2000 UCON ™ 50- 23.2000 HB-5100 UCON ™ OSP- 66.9000 76.8000 18 UCON ™ OSP- 76.7000 32 UCON ™ OSP- 73.1000 100.0000 68 Synalox OA60 90.0000 Capped 68.3000 UCON ™ OSP- 18 (97060) Capped 77.6 UCON ™ OSP- 32 (97061) Capped 85.6 UCON ™ OSP- 46 (97062) SYNALOX ™ 70.5 OA-25 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

TABLE III Test Results of Various Base Fluids Test Results C. Ex. C. Ex. C. Ex. Test C. Ex. A Ex. 1 Ex. 2 C. Ex. B C. Ex. C C. Ex. D C. Ex. E F* G* H* C. Ex. I Kinematic Viscosity 12 11.7 11.7 11.7 12.03 11.7 11.3 NM NM NM 11.71 at 100° C. Dynamic Viscosity 11.68 10.5 10.4 10.6 11.06 10.7 10.2 NM NM NM 10.75 at 100° C. Dynamic Viscosity 57.5 51.4 50.2 55.7 62.2 68.7 61.5 NM NM NM 57.3 at 40° C. Viscosity Index (V.I.) 221 217 221 199 186 155 168 NM NM NM 196 −(minus) 40° C. 52800 31199 20994 49825 101000 94000 NM NM NM 75282 Dynamic Viscosity (cP) Solubility Soluble Soluble Soluble Slightly Soluble Soluble N/A Turbid Turbid Turbid Soluble turbid Traction coefficient at 0.027 0.028 0.03 Not — — 0.043 — — — — 80° C. and 500 mm/s evaluated due to insolubility Traction coefficient at 0.021 0.021 0.022 Not — — 0.037 — — — — 120° C. and 500 mm/s evaluated due to insolubility *These examples were not measured due to insolubility. NM = “not measured”.

As described in Table III above, Comparative Example A (C. Ex. A) shows the viscometrics and traction coefficients of standard UCON™ 50-HB-260 with UCON™ 50-HB-400 and compares these properties to an UCON™ OSP-68 base fluid highlighted in Comparative Example E (C. Ex. E). These comparisons are made for similar viscosity grades (75W85) which is dictated, in part, by kinematic viscosity at 100° C. UCON™ OSPs, in general, have about 15% to about 20% higher dynamic viscosity at 40° C. compared to a UCON™ 50-HB fluid when the kinematic viscosities are matched at 100° C. UCON™ OSPs also have about 75% to about 80% higher dynamic viscosity at −40° C. and about 60% higher traction coefficients when compared to UCON™ 50-HB fluids.

A mixture of a similar viscosity UCON™ OSP and UCON™ 50-HB fluids was tested and the results of which are highlighted in Comparative Example C (C. Ex. C). The mixture improved the V.I. of the combination fluid when compared to UCON™ OSP alone but didn't have any impact on dynamic viscosity at 40° C. and −40° C. When lower viscosity UCON™ OSP (UCON™ OSP-18) and higher viscosity UCON™ 50-HB fluids are combined, the resulting fluid provides some unique low temperature viscometrics as well as the traction coefficients of UCON™ 50-HB base fluids are retained. Example 1 (Ex. 1) and Example 2 (Ex. 2) of the present invention highlight the properties of these unique combinations of fluids. At approximately 67/33 weight % of UCON™ OSP-18 and UCON™ 50-HB-2000 which is required to achieve a kinematic viscosity of 11.7 cSt at 100° C., the resulting fluid has a VI of 217 which is similar to that of the UCON™ 50-HB-260+UCON™ 50-HB-400 (221) fluid. Also this combination provides 11% lower dynamic viscosity at 40° C. and 40% lower dynamic viscosity at −40° C. These properties are further enhanced when UCON™ OSP-18 is mixed with even a higher molecular weight UCON™ 50-HB-5100 as highlighted in Ex. 2.

Surprisingly, it has been found that higher molecular weight UCON™ OSPs (e.g., UCON™ OSP-32 and above) are not soluble in the higher molecular weight UCON™ 50-HB-2000 fluids as highlighted in Comparative Example B (C. Ex. B). Thus, dodecanol initiated PO/BO copolymers with molecular weight less than 550 Da and butanol initiated EO/PO copolymers with molecular weight greater than 2,660 Da is a unique combination found to provide benefits in terms of improved low temperature viscometrics and lower traction coefficients. When combining capped UCON™ OSPs with UCON™ 50-HB-2000 fluids, the resulting mixtures are not soluble at room temperatures. This is highlighted in Comparative Example G [C. Ex. G] to Comparative Example I (C. Ex. I).

A combination of lower molecular weight butanol initiated BO homopolymer (SYNALOX™ OA-25) and higher molecular weight butanol initiated EO/PO copolymer (UCON™ 50-HB-2000) were used as shown in C. Ex. I. This combination was found to be miscible but the composition of C. Ex. I did not provide as good of a low temperature viscometrics compared to the Examples of the present invention.

Examples 3-4 and Comparative Examples J-L

Table IV describes the composition of various base fluids. Table V describes the results of evaluating the several formulations with the components listed in Table IV. Table IV highlights the kinematic and dynamic viscosities, viscosity index, low temperature dynamic viscosity, solubility and traction coefficients of different combinations of base fluids. All of the fluids have a target viscosity of 11.7 cSt at 100° C.

TABLE IV Various Base Fluids C. Ex A Ex. 1 Ex. 3 C. Ex. J C. Ex. K Ex. 4 C. Ex. L Components Wt % Wt % Wt % Wt % Wt % Wt % Wt % UCON ™ 50-HB-260 80.5000 UCON ™ 50-HB-400 19.5000 UCON ™ 50-HB-660 56.5000 UCON ™ 50-HB-2000 33.1000 39.0000 SYNALOX ™ 55-150B 40.0000 48.0000 SYNALOX ™ 40D300 33.0000 UCON ™ OSP-12 61.0000 52.0000 UCON ™ OSP-18 66.9000 43.5000 60.0000 67.0000 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00

TABLE IV Test Results of Various Base Fluids Test Results Test C. Ex. A Ex. 1 Ex. 3 C. Ex. J C. Ex. K Ex. 4 C. Ex. L Kinematic Viscosity 12 11.7 11.6 12 11.04 11.1 at 100° C. Dynamic Viscosity 11.68 10.5 10.3 11 10 10 at 100° C. Dynamic Viscosity 57.5 51.4 48 56 49.9 47 at 40° C. Viscosity Index (V.I.) 221 217 229 211 209 225 minus 40° C. Dynamic 52,800 31,199 Viscosity (cP) Solubility Soluble Soluble Soluble Soluble Soluble Soluble Not soluble

The impact of even lower molecular weight UCON™ OSP such as the UCON™ OSP-12 and a combination of UCON™ 50-HB-2000 were evaluated. The properties of this combination are show in Example 3 (Ex. 3) in Table V. This combination further improves the V.I. from 217 to 229 and reduces the low temperatures viscosities even further compared to Ex. 1. In order to evaluate the impact of using lower molecular weight 50/50 EO/PO copolymer, a blend of UCON™ OSP-18 and UCON™ 50-HB-660 (Molecular weight of 1,590 and 26 cSt viscosity at 100° C.) were produced labeled as Comparative Example J (C. Ex. J) in Tables IV and V. This blend renders a V.I. of 209 and its 40° C. dynamic viscosity is slightly lower compared to C. Ex. A. Therefore, no significant benefits were achieved in terms of the V.I. and in terms of the low temperature viscosities.

To evaluate the impact of change in EO/PO ratios and choice of initiator, production of a blend of UCON™ OSP-18 and SYNALOX™ 40-D300 was attempted as described in Comparative Example L (C. Ex. L). This blend was insoluble with UCON™ OSP suggesting that the EO/PO ratio cannot be increased beyond 50/50 unless changes are made in the initiators. In order to assess the impact of molecular weights between 1,500 Da and 2,600 Da for the EO/PO structures, a blend of SYNALOX™ 55-150B was made with UCON™ OSP-18 (Comparative Example K) and UCON™ OSP-12 (Example 4). It was found that similar to the UCON™ OSP-18 and UCON™ 50-HB-660 blends (C. Ex. J) a blend of SYNALOX™ 55-150B and UCON™ OSP-18 had a V.I. of 209 and had no significant advantage in terms of reducing the dynamic viscosity at 40° C. However, a blend of SYNALOX™ 55-150B and UCON™ OSP-12 (Example 4) did provide a significantly higher V.I. of 225 and also a dynamic viscosity at 40° C. which was significantly lower compared to the baseline.

Overall, a combination of multiple blends of base oils including those that include UCON™ OSP-12 and/or UCON™ OSP-18 with UCON™ 50-HB-2000, UCON™ 50-HB-5100 and/or SYNALOX™ 55-150B provided V.I. of above 217, 40° C. dynamic viscosities that were 10-15% lower than individual UCON™ 50-HB fluids, similar traction coefficients as 50/50 EO/PO fluids and 10-50% lower dynamic viscosity compared to a baseline 50/50 EO/PO copolymer of similar kinematic viscosity at 100° C. 

1. A lubricant composition comprising: (a) a first low viscosity polyalkylene oxide based fluid with a first alcohol as an initiator; wherein the first low viscosity polyalkylene oxide based fluid is copolymer formed with a combination of propylene oxide and butylene oxide and has a number average molecular weight of less than about 600; and (b) a second high viscosity polyalkylene oxide based fluid with a second alcohol as an initiator; wherein the second high viscosity polyalkylene oxide based fluid is a copolymer formed with 50/50 or 45/55 ethylene oxide/propylene oxide and has a number average molecular weight of 1,590 to 3,930; and wherein the first low viscosity polyalkylene oxide based fluid is different from the second high viscosity polyalkylene oxide based fluid. 2.-4. (canceled)
 5. The composition of claim 1, wherein the first low viscosity propylene oxide/butylene oxide combination based fluid is an about 50/50 propylene oxide/butylene oxide based fluid.
 6. The composition of claim 1, wherein the first alcohol initiator for the first low viscosity polyalkylene oxide based fluid is dodecanol.
 7. (canceled)
 8. The composition of claim 1, wherein the second alcohol initiator for the second high viscosity polyalkylene oxide based fluid is butanol.
 9. The composition of claim 1, wherein the molecular weight of the first low viscosity polyalkylene oxide based fluid is from about 300 to about
 600. 10. (canceled)
 11. The composition of claim 1, wherein the concentration of the first low viscosity polyalkylene oxide based fluid is from about 40 weight percent to about 80 weight percent.
 12. The composition of claim 1, wherein the concentration of the second high viscosity polyalkylene oxide based fluid is from about 20 weight percent to about 60 weight percent.
 13. The composition of claim 1, wherein the lubricant composition has an 11 to 12 centistokes viscosity at 100° C. has a viscosity index of greater than about 215 to about 225; a dynamic viscosity of lower than about 40,000 centipoise at a temperature of −40° C.; in the absence of a pour point depressant or a viscosity index improver.
 14. A process for manufacturing a lubricant composition comprising admixing: (a) a first low viscosity polyalkylene oxide based fluid with a first alcohol as an initiator, wherein the first low viscosity polyalkylene oxide is copolymer formed with a combination of propylene oxide and butylene oxide and has a number average molecular weight of less than about 600; and (b) a second high viscosity polyalkylene oxide based fluid with a second alcohol as an initiator, wherein the second high viscosity polyalkylene oxide is a copolymer formed with 50/50 or 45/55 ethylene oxide/propylene oxide and has a number average molecular weight of 1,590 to 3,930; wherein the first low viscosity polyalkylene oxide based fluid is different from the second high viscosity polyalkylene oxide based fluid.
 15. The process of claim 14, wherein the lubricant composition having an about 11 centistokes to about 12 centistokes viscosity at 100° C. has a viscosity index of greater than about 215 to about 225; a dynamic viscosity of lower than about 40,000 centipoise at a temperature of −40° C.; in the absence of a pour point depressant or a viscosity index improver.
 16. A driveline fluid made from a lubricant composition comprising: (a) a first low viscosity polyalkylene oxide based fluid with a first alcohol as an initiator; wherein the first low viscosity polyalkylene oxide based fluid has a number average molecular weight of less than 600; and (b) a second high viscosity polyalkylene oxide based fluid with a second alcohol as an initiator; wherein the second high viscosity polyalkylene oxide based fluid has a number average molecular weight greater than 600; and wherein the first low viscosity polyalkylene oxide based fluid is different from the second high viscosity polyalkylene oxide based fluid.
 17. The driveline fluid of claim 16, wherein the first low viscosity polyalkylene oxide based fluid has a number average molecular weight of less than 580; and wherein the second high viscosity polyalkylene oxide based fluid has a number average molecular weight greater than 1,500.
 18. The driveline fluid of claim 16, wherein the first low viscosity polyalkylene oxide based fluid is a combination of a propylene oxide and a butylene oxide.
 19. The driveline fluid of claim 16, wherein the second high viscosity polyalkylene oxide based fluid is a combination of an ethylene oxide and a propylene oxide.
 20. The driveline fluid of claim 16, wherein the lubricant composition has an 11 to 12 centistokes viscosity at 100° C. has a viscosity index of greater than 215 to 225; a dynamic viscosity of lower than 40,000 centipoise at a temperature of −40° C.; in the absence of a pour point depressant or a viscosity index improver. 